In recent years, non-contact power feeding of an electromagnetic induction type using a coil has been studied as a method of charging electric vehicles (EVs). While an enameled wire having a conducting body covered with an insulation film is wound around a coil used in the non-contact power feeding of the electromagnetic induction type, it is necessary to supply a large current having a high frequency in the case of the non-contact power feeding for EVs, and therefore a litz wire having a plurality of enameled wires (strands) twisted together is used. One reason for this is that increase in alternating-current resistance due to the skin effect and the proximity effect specific to high frequency can be limited when a litz wire is used.
To a terminal part of such a litz wire, a terminal metal fitting is connected. Various terminal metal fittings are available, and an example of known terminal metal fittings is a closed-barrel type terminal metal fitting having a cylindrical wire barrel part (hereinafter referred to as “closed barrel terminal”). When connecting a litz wire to the closed barrel terminal, a terminal part of the litz wire is inserted into a wire barrel part, and is firmly fixed thereto.
In the case of a litz wire in which the number of strands twisted together is small, it is possible to adopt fusing (thermal caulking) in which, after a terminal part of the litz wire is inserted to the wire barrel part, electric heating is performed on the terminal metal fitting, to pressure fix the litz wire and the wire barrel part while vaporizing an insulation film. However, since a litz wire (for example, a copper litz wire of about 8 mm2 or an aluminum litz wire of about 13 mm2) which is used for a non-contact power feeding coil for EVs and has a large number of strands twisted together has a large thermal capacity, fusing cannot be applied to such a litz wire. One reason for this is that it is difficult to remove insulation films in the center part of such a litz wire by fusing, and when the heating temperature is increased so as to remove the insulation films in the center part, the conducting body may possibly be melted.
Under such circumstances, conventionally, a method has been applied in which a terminal part of a litz wire is connected to a wire barrel part of a terminal metal fitting by soldering. In such a terminal connection method using soldering, after the insulation film of a terminal part of litz wire 1 is mechanically or chemically removed in advance, litz wire 1 is inserted to wire barrel part 22 of terminal metal fitting 2, and temporarily fixed (retained) by compression, as illustrated in FIG. 1. Then, by pouring solder S having a high temperature from the front end side of wire barrel part 22, litz wire 1 and terminal metal fitting 2 are electrically connected together while melting the remaining insulation films (insulation films in the center part of litz wire 1 in particular).
In addition, the terminal part of litz wire 1 may be preliminarily soldered in order to facilitate the insertion of the terminal part of litz wire 1 to wire barrel part 22.